#version 450

// Sample the glyph atlas (R = coverage 0..1) and mix the cell's bg up to its fg
// by that coverage. Fully opaque: the swapchain is SDR, no blending needed.

layout(set = 2, binding = 0) uniform sampler2D u_atlas;

layout(location = 0) in vec2 v_uv;
layout(location = 1) in vec3 v_fg;
layout(location = 2) in vec3 v_bg;
layout(location = 3) in vec2 v_cell_uv;
layout(location = 4) flat in uvec4 v_effect;

layout(location = 0) out vec4 o_col;

float cellNoise(uint serial, uint col, uint row) {
    uint x = serial ^ (col * 0x9e3779b9u) ^ (row * 0x85ebca6bu);
    x ^= x >> 16;
    x *= 0x7feb352du;
    x ^= x >> 15;
    x *= 0x846ca68bu;
    x ^= x >> 16;
    return float(x & 0xffffu) / 65535.0;
}

float asciiGlyph(vec2 uv, int glyph) {
    vec2 p = uv * 2.0 - 1.0;
    float thin = 0.12;
    float dotShape = 1.0 - smoothstep(0.10, 0.20, length(p - vec2(0.0, 0.45)));
    float barH = 1.0 - smoothstep(thin, thin + 0.08, abs(p.y));
    float barV = 1.0 - smoothstep(thin, thin + 0.08, abs(p.x));
    if (glyph == 0) return dotShape;
    if (glyph == 1) return max(dotShape, 1.0 - smoothstep(0.10, 0.20, length(p + vec2(0.0, 0.45))));
    if (glyph == 2) return max(barH, barV);
    if (glyph == 3) {
        float d0 = 1.0 - smoothstep(thin, thin + 0.08, abs(p.x - p.y));
        float d1 = 1.0 - smoothstep(thin, thin + 0.08, abs(p.x + p.y));
        return max(max(d0, d1), max(barH, barV));
    }
    if (glyph == 4) {
        float rails = max(
            1.0 - smoothstep(thin, thin + 0.08, abs(abs(p.x) - 0.34)),
            1.0 - smoothstep(thin, thin + 0.08, abs(abs(p.y) - 0.34))
        );
        return rails;
    }
    float ring = 1.0 - smoothstep(thin, thin + 0.08, abs(length(p * vec2(0.8, 1.0)) - 0.48));
    return max(ring, glyph == 6 ? dotShape : 0.0);
}

void main() {
    float a = texture(u_atlas, v_uv).r;
    bool oldLayer = (v_effect.x & 0x80000000u) != 0u;
    uint effect = v_effect.x & 0x7fffffffu;
    float progress = clamp(uintBitsToFloat(v_effect.y), 0.0, 1.0);
    uint cellCol = v_effect.w & 0xffffu;
    uint cellRow = v_effect.w >> 16;
    float noise = cellNoise(v_effect.z, cellCol, cellRow);

    vec3 cell = mix(v_bg, v_fg, a);

    // 3 = data dissolve. Changed cells retain the frozen old cell until their
    // stable threshold, then atomically become the new cell. Exact endpoints
    // mirror panel_animation.dissolveRevealed, including the zero hash.
    if (effect == 3u) {
        bool reveal = progress >= 1.0 || (progress > 0.0 && noise < progress);
        if (oldLayer ? reveal : !reveal) discard;
        o_col = vec4(cell, 1.0);
        return;
    }

    // 4 = ASCII materialization. A diagonal/noise threshold matches the TTY
    // compositor's idea: cells briefly become punctuation, then their real
    // atlas glyph arrives. The procedural marks keep the GUI implementation
    // entirely shader-side.
    if (effect == 4u) {
        if (progress <= 0.0) {
            if (!oldLayer) discard;
            o_col = vec4(cell, 1.0);
            return;
        }
        if (progress >= 1.0) {
            if (oldLayer) discard;
            o_col = vec4(cell, 1.0);
            return;
        }
        float diagonal = float((cellCol + cellRow * 2u) % 17u) / 17.0;
        float threshold = noise * 0.72 + diagonal * 0.28;
        if (progress >= threshold) {
            if (oldLayer) discard;
            o_col = vec4(cell, 1.0);
            return;
        }
        if (progress + 0.22 >= threshold) {
            if (oldLayer) discard;
            int glyph = int(floor(noise * 7.0));
            float ink = asciiGlyph(v_cell_uv, min(glyph, 6));
            vec3 dimInk = mix(v_bg, v_fg, 0.62);
            o_col = vec4(mix(v_bg, dimInk, ink), 1.0);
            return;
        }
        if (!oldLayer) discard;
        o_col = vec4(cell, 1.0);
        return;
    }

    // FreeType's hinted grayscale bitmap is already the intended coverage.
    // Preserve it exactly; weight-changing gamma hacks blur small stems.
    o_col = vec4(cell, 1.0);
}